Polyimide has various excellent properties such as thermal, mechanical and electric properties, chemical resistance, gas separation properties and processability, therefore polyimide is industrially and widely utilized as a high performance material for microelectronic materials, molding materials, films, etc. The polyimides used as such conventional high performance materials have been linear polyimides which are generally obtained by reacting: an aromatic tetracarboxylic dianhydrides such as pyromellitic dianhydride or biphenyltetracarboxylic dianhydride, and an aromatic diamines such as diaminodiphenyl ether.
On the other hand, a silicon resin (silicone) is also excellent in thermal stability, electric properties, chemical resistance and surface properties (hydrophobicity, adhesive property), and is used in various applications as industrial materials.
Heretofore, various siloxane-modified polyimides having silicon atoms and various siloxane structures in the molecule thereof have been developed as materials having both excellent properties of polyimide and silicon. For example, a siloxane-modified polyimide having a lower modulus than polyimide and excellent in thermoplasticity, adhesive property is widely used for films for microelectronic materials, heat-resistant adhesives, and etc.
Various methods are proposed for introducing various siloxane structures in a polyimide molecule, and of those, a method of copolymerization with a diaminosiloxane compound at the time of synthesis of polyimide is a typical method (see Non-Patent Document 1 and Patent Document 1). Using this method, there are also reported a polyimide copolymer having a micro-separated structure (see Patent Document 2 and Non-Patent Document 2) and a siloxane-containing polyimide soluble in organic solvent (see Patent Documents 3 and 4), obtained by reacting an aromatic tetracarboxylic dianhydride, an aromatic diamine and a diaminosiloxane compound.
However, in such conventional siloxane-containing polyimides, the constitutive polyimide is linear, and the linear polyimide basically has only two end groups when any specific structure such as graft is not introduced thereinto. Therefore, the conventional siloxane-containing polyimides comprising such a linear polyimide are difficult to modify with various functional groups and to produce multifunctional polymers having various functions.    Patent Document 1: JP-A-62-223228    Patent Document 2: JP-A-2-91124    Patent Document 3: U.S. Pat. No. 3,325,450    Patent Document 4: U.S. Pat. No. 3,740,305    Non-Patent Document 1: J. E. McGrath et al., Advances in Polymer Science, Vol. 140, p. 61    Non-Patent Document 2: Yamada, Yasuharu, and two others, “Property of Silicon-Containing Polyimide, and Application Thereof”, monthly Polymer Processing, published by Kobunshi Kankokai, February 1997, Vol. 46, No. 2, pp. 2-11